The present invention relates to a method for cutting hollow-cored concrete slabs.
The present invention also concerns an apparatus for implementing the method.
In the production of hollow-cored concrete slabs, the slabs are conventionally cast on long beds using a continuous slip-forming extrusion method. In their typical form, the cored slabs are prestressed structures cast from relatively stiff mixes. Immediately after completion of the casting phase, openings and recesses are worked into the slabs according to the individual specifications of construction drawings. Working is performed using manual methods by first measuring the elements with a tape measure and marking the cutting points of elements. Referencing the cutting point, the position of each opening is measured and marked, after which manual tools are used to scrape the openings free of unhardened mix that is then placed in a waste mix container. In some cases, the ends of slabs are trimmed immediately after the casting operation prior to the hardening of the mix. The immediate cutting is most typically performed using manual tools, e.g., a circular saw.
In some cases the immediate cutting is made over such a wide length (10 . . . 20 cm) that the ends of hollow cores are visible from the cutting point, allowing the ends to be filled with concrete mortar or mix using manual methods.
In the next phase the entire set of cored slabs is covered with a protective blanket until the final setting of the concrete. When the concrete has attained a sufficient strength, it is possible to cut the prestressing tendons at the ends of the slabs. Most typically, the slabs are cut by using a circular saw with a diamond-tipped blade, which is capable of cutting the set concrete, in addition to the tendons. Next, the elements can be transferred from the casting bed to be bundled and then placed into final storage until they are later transported to the construction site. Prior to storage, however, the ends of the hollow cores are always stoppered by a suitable type of plug so that the jointing mix applied at the construction site to the joint between the element ends is not able to flow into and fill up the cores. Consequently, the stopper plugs of the hollow cores in the cored element, in practice, perform as casting plugs, but they may also be applicable as supports for the wall constructions resting on the ends of cored slab. The type of plug conventionally used is a cast concrete plug or a detachable, cup-shaped, molded plastic plug.
Of the plugging methods described above, a disadvantage to be pointed out is that of the high proportion of manual labour required. Each plugging operation calls for a dedicated work phase, and, also, quite frequently, the use of a dedicated and expensive plugging material.
The present invention aims to overcome the disadvantages found in prior-art techniques and to provide an entirely novel method and apparatus for cutting prestressed hollow-cored concrete slabs.
The method is based on an instant cutting of hollow-cored slabs immediately after the casting phase while simultaneously filling the ends of the hollow cores using the excess mix from the cutting phase as a filler.
The method and apparatus of the present invention provides remarkable advantages. When using the method in accordance with the invention, the labour-intensive sawing phase is shortened and the manual labour-requiring operation of filling the core ends is replaced by the filling of the core ends already in conjunction with the instant cutting phase.